Sure, I know how to recover from it, but I have two of these in my config for redundancy, and both started reboot loop within 4 hours of each other which completely defeats the point of redundancy.
The question is vague and there are no valid clues,
I would never have used a version higher than 7.16.2 in production in devices that must necessarily have v7 because they are not supported by v6.
Given the distance and the same problem,
I could forcefully deduce that some configuration, applied on one and then copied to the other, crashed the system and ruined the filesystem,
or that they both had the same username and password, and “someone” did some work on them…